Multiplexers, such as duplexers, using a filter are employed in mobile communication terminals such as mobile phones. Japanese Patent Application Publication No. 2012-10164 (Patent Document 1) discloses connecting a resonator including an Interdigital Transducer (IDT) between a filter and a common terminal in a duplexer including two filters.
When a resonator including an IDT is employed as disclosed in Patent Document 1, the connection of the resonator between a first filter, which has a higher passband, of the two filters and the common terminal increases the loss of the resonator in the higher passband.